In a conventional advance-retreat position detection device disclosed in Japanese Unexamined Utility Model Application Publication No. H3-42706 and illustrated in FIG. 8, herein, focusing on the change in pressure of a gas M1 in a chamber M2 in accordance with an advance-retreat position of an operating member M3 in the chamber M2, the abovementioned pressure is detected by a pressure detector M4, and, thereby, the advance-retreat position of an operation member M3 is detected by an advance-retreat position detector M5; and focusing on the influence that high temperature in the chamber M2 exerts on the abovementioned pressure, temperature detector M6 detects that temperature, and a temperature corrector M7 corrects the temperature at the advance-retreat position of the operation member M3 on the basis of the temperature output, so that an accurate stroke amount is detected as a result.
Known front fork suspensions include suspensions in which front forks are disposed on the left and right, each front fork being configured in the form of a mechanical spring and a damper integrated with each other, and also suspensions in which the functions of the spring and the damper are divided between the left and right front forks.
The springs used in front forks of the latter type include mechanical coil springs and air springs.
Front forks that utilize air springs are configured in the form of two air spring chambers, namely an outer air spring chamber comprising an inner space of a vehicle body-side (first) tube and an inner space of an axle-side (second) tube, and an inner air spring chamber that is partitioned, from the outer air spring chamber, through sliding of a piston, which is mounted to the vehicle body-side tube, within a guide cylinder that is provided in the axle-side tube. The volume of the outer air spring chamber increases or decreases as a result of changes in the total length of the vehicle body-side tube and the axle-side tube accompanying the stroke operation of the suspension, while the volume of the inner air spring chamber increases or decreases as a result of displacement of the piston within the guide cylinder. The air in the air spring chambers undergoes repeated compression and expansion as a result of the abovementioned volume increases or decreases. This compression and expansion of air translates into rises in the temperature in the air spring chambers, as well as rises in the pressure in the air spring chambers on account of the increases in temperature. These rises and drops in the pressure in the air spring chambers that accompany rises in temperature may alter the designed functionality of the air spring, and may detract from the suspension effect in the vehicle. Therefore, it would be conceivable, on the basis of Japanese Unexamined Utility Model Application Publication No. H3-42706, to measure the temperature and/or pressure in the outer air spring chamber and to use an advance-retreat position detection device that adjusts the stroke amount according to changes in the temperature and/or pressure.
In the advance-retreat position detection device of Japanese Unexamined Utility Model Application Publication No. H3-42706, however, the stroke amount is detected through measurement of the pressure and temperature of the outer air spring chamber having a greater volume than an inner air spring chamber. Accordingly, the precision of stroke detection is low. That is, the volume of the outer air spring chamber is larger than that of the inner air spring chamber, and hence the volume change that arises through advance and retreat of the piston that modifies the volume of the inner air spring chamber and the outer air spring chamber is relatively small. Therefore, pressure fluctuations are small, and the pressure and temperature changes measured by the sensors are likewise small. It is thus found that detection precision of the stroke amount is not very good. Further, pressure and temperature are measured in only one spring chamber. This was problematic in that, as a result, it was not possible to detect pressure leaks (air leaks) between the inner air spring chamber and the outer air spring chamber, or between the outer air spring chamber and outside air, and it was not possible to detect immediately the occurrence of anomalies in the air tightness of the outer air spring chamber and the inner air spring chamber. The pressure detector and the temperature detector being configured in the form of one set alone was a further drawback, since in that case the stroke amount cannot be detected if one of the detectors malfunctions.